Isolated cells from rat anterior pituitary glands are studied in vitro to compare their physiology in old vs. mature male and female rats. Production of TSH, prolactin, and gonadotropins (LH and FSH) are studied after treatment with specific stimulatory and inhibitory compounds, included TRH, LHRH, estrogen, dopamine, and iontophores. Deranged and altered function of aged rat pituitary cells in vitro has been found. Pretreatment of old and young rats for up to 24 hours with pulsatile doses of LHRH does not restore function of cells derived from old rats to levels observed for younger animals. Similarly, enhanced tranmembrane transport of calcium ion with iontophore A23187 does not reverse the age-related defect in LH secretion. Data support our prior results suggesting an intrinsic age-related derangement in pituitary gonadotropic function. We have also described enhanced basal and estrogen stimulated Prl secretion by pituitary cells from old female rats, an increase in function disproportionate to the smaller increase in lactotrope number in aging rat pituitary glands. We have begun an investigation of the role of oxygen free radicals in the phenomenon of "in vitro" aging of Leydig (testosterone- secreting) cells. Preliminary experiments have demonstrated isolated Leydig cells to have lower activity of the protective enzyme, copper-zinc superoxide dismutase, than cells derived from seminiferous tubules, which normally surround (and may protect) Leydig cells from superoxide damage in vivo.